What happened

A vessel experienced a cargo pump bearing failure when she was discharging cargo at the discharge port. The pump was out of use and this resulted in moving out the vessel from the berth. Cargo was transferred from one tank to other after which the vessel was re-berthed for discharging the remaining cargo.
The failure caused a delay to the vessel as well as commercial and reputation loss to owners.

Cause of failure

The pumps were recently overhauled during the vessel docking. The bearings and seals were renewed. Upon investigation for the cause of bearing failure by the technicians, it was found that the grease which was used for the bearing was of not the correct grade. The vessel was using normal bearing grease, but the maker recommended high viscosity ones. Used grease properties: Viscosity at 400C 120 mm2/sec. Operating temperature -30 to 1200C.
Maker recommended grease viscosity at 400C is 160-180mm2/sec.
Low viscosity grease tends to melt faster at high temperature and leak out of bearing race, subsequently causing dry running of bearing.
The low viscosity grease has melted and leaked out of the bearing case. The bearing seized due to lack of lubrication. There was a lack of reporting and timely action by ship staff, the cargo pump was let to run at higher abnormal temperatures which resulted in bearing failure. alt text
Grease had melted and leaked out of the housing
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Lower V-Ring was completely melted and missing. Oil seal and Teflon bush were deformed and melted
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Bearings, Coupling and Housing
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The roller bearing inner race was seized/welded onto the coupling shaft

Corrective actions

  • Make sure that the grade of grease being used onboard for the cargo pumps is one of the grades recommended by pump makers.
  • Follow the greasing interval and quantity of grease as per manual.
  • Stencil the correct grade of grease that should be used to be used near the bearing housing/greasing point.
  • Bearing temperature must be recorded during the cargo pump operations

posted 26 Apr '18, 04:28

April 26, 2018, 4:28 a.m.
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